1. Field of the Invention
The present invention relates to a tone mapping method and image processing device, and more particularly, to a tone mapping method and image processing device capable of adjusting image contrast according to both image luminance and sharpness, and controlling the degree of image adjustment via a weighted operation.
2. Description of the Prior Art
Digital images can be post-processed to attain more ideal image characteristics. For example, when capturing images using a digital camera, under-exposure and low overall image contrast may occur due to a lack of ambient lighting. To correct for this, conventional tone mapping techniques can respectively map each luminance value in the image to a new luminance value to adjust the overall contrast of the image. Image equalization is one example of a conventional tone mapping method that can achieve ideal image contrast by redistributing luminance values in an image, such that the luminance values are evenly spread over a luminance range. Conventional image equalization, however, simply brightens the relatively high luminance values in the image and darkens the relative low luminance values; therefore, over-compensation often occurs, meaning bright areas may be over-exposed or dark areas under-exposed. This results in a loss of detail in those areas.
Conventional equalization also cannot control different degrees of adjustment for parts having different sharpness values in an image, which often results in a visibly discontinuous contour effect in the processed image. Users also need to manually modify image characteristics such as S-curves to change a dynamic range of the image if the level of tone mapping adjustment needs to be adjusted, which is time-consuming and inconvenient.
Therefore, the conventional image tone mapping method needs improvement.